1. Technical Field of the Invention
This invention relates generally to the dissociation of molecules into atoms, their transport through a solid membrane and their subsequent desorption by electron or photon desorption. In particular, it relates to a device for the production of a high purity, neutral hyperthermal atomic beam generator capable of producing e.g. atomic oxygen, nitrogen, hydrogen, and other species, the device being compact and ultrahigh vacuum (UHV), high vacuum, and rough vacuum (&lt;10.sup.-3 Torr) compatible.
2. Description of Related Art
The composition of the atmosphere within the orbital envelope (200-1000 km) combined with the orbital velocity (8 km s.sup.-1) results in a flux of hyperthermal atomic oxygen (E.about.5 eV, v.about.10.sup.15 cm.sup.-2 s.sup.-1) impinging on spacecraft surfaces. The extreme reactivity of atomic oxygen leads to numerous chemical unions with other species to form, for example, CO, CO.sub.2, H.sub.2 O, O.sub.2, SO.sub.2, and NO.sub.2. Further, the high chemical reactivity of this O atom flux has caused substantial degradation of organic materials on board the Shuttle and suggests that materials on the proposed Space Station Freedom, the composites used in large space structures, exterior coatings on the optics of the Hubble Space Telescope, the UV telescopes, and future laser communications systems may have substantially reduced lifetimes. It is therefore essential to study the reactivity of these materials to atomic oxygen in ground based laboratories. In order to conduct such laboratory experiments, an atomic oxygen beam generator is required that can accurately simulate the flux and energy (within the appropriate vacuum environment) of the vehicle experience in orbit. In addition to oxygen atom reactions that the vehicle experiences in orbit, and to oxygen atom reactions with spacecraft materials, such a beam system as well as other atomic beam sources would also be of importance in the calibration of mass spectrometers and other detection systems that would be used for mapping the density of gas constituents within the orbital envelope. Such calibration is essential to make accurate measurements of the representative gas environment within the orbital envelope. A pure, well behaved O beam would also be useful for producing an ordered oxide layer for growth of compound semiconductors and superconductors. Methods of thin film growth, such as molecular beam epitaxy (MBE), could fully utilize a directed O atom beam to grow desired layers without the residual contaminating effects of backfield O.sub.2 or the limitations of dissociative adsorption as well as N and H beams for producing high purity nitrides and hydrides. In addition, atomic halogen beams could be used to etch semiconductor and other materials in a uniform, well controlled manner. Other areas of interest, such as fundamental surface science and chemical kinetics, are obvious. It is also possible to generate beams of molecular particles with the present invention although the primary use for the present invention is the production of single atom particles. For simplicity, the term atom beam, when applied to the present invention, is assumed to include the whatever particle is desired from the source even if the desired particles are molecules. There are several systems that are presently available for the above applications, but they are, in general, quite large, expensive, not ultrahigh vacuum (UHV) compatible, and require the samples to be brought to their location.
In U.S. Pat. No. 4,828,817 a process for generating a pure atomic oxygen beam was disclosed, which process obviated many of the disadvantages associated with the systems of the prior art. Still lacking, however, was a simple workable, practical device that is small and designed for UHV applications.